An example of the construction of a conventional liquid crystal display device is shown in FIG. 2. FIG. 2 shows a diagrammatic side view of an ordinary liquid crystal display device that is composed of, as shown in the figure, a backlight 11 of an edge light type on the furthest back surface and, in the order from the furthest back surface, a light introductive plate 12 for injecting light from the back light toward the surface, a scattering sheet 13 for uniformly dispersing brightness of the light, and one or plural light-tuning sheet (light tuning film) 14 having a function for condensing the uniformly dispersed light by the scattering sheet to a given direction or alternatively a function for selectively transmitting or reflecting a specific polarized light. Light passing through these films is injected to a liquid crystal cell 17 interposed between a pair of polarizing plates 15 and 16. In the figure, 18 denotes a cooled cathode fluorescent tube as light source and 19 a reflective sheet.
In the liquid crystal display device, usually the light tuning film 14 and the backside polarizing plate 15 located on the side of the liquid crystal cell are especially not bonded with a binder or the like so that a slight gap exists between both. This light tuning film 14 is made of an acrylic resin, a polyester, a polycarbonate or the like, but these materials are rather larger in stretching or shrinking caused by change in temperature so that the light tuning film 14 elongated by heating due to ambient circumstance, backlight or the like is brought into contact with the backside polarizing plate 15 to cause non-uniformity in display in circumferential areas of image. In some of the light tuning films, there exists a unique brightness non-uniformity, thus bringing about deterioration in their display quality. With regard to the above-mentioned light-tuning film, JP-A-10-240143 (“JP-A” means unexamined published Japanese patent application) describes that an irregularity (concavo-convex structure) that is formed by transparent particles on the surface of the light-tuning film prevents deterioration of the display quality when dew condensation occurs in the gap between a light-tuning film and a backside polarizing plate, and consequently they adsorb each other via dew droplets.
However, the polarizing plate still fails to prevent unevenness of the display that occurs when the polarizing plate contacts a light-tuning film due to thermal expansion, and unevenness of the brightness that is peculiar to the light-tuning film. Further, the polarizing plate has a disadvantage of reducing transmittance of the back light. To prevent unevenness of the brightness of the light-tuning film, it is conventionally proposed to use another scattering film between the light-tuning film and a liquid crystal cell. Generally, however, since the scattering film has a haze, the transmittance tends to be lowered. Accordingly, it is difficult to avoid the possibility that reduction in brightness of the display may be caused by giving matt property thereto.
Accordingly, an object of the present invention is to provide a film having a high transmittance that is able to prevent occurrence of both unevenness of the display due to thermal expansion of the light-tuning film, and unevenness of the brightness that is peculiar to the light-tuning film, as mentioned above. Another object of the present invention is to provide a polarizing plate using a film having a high transmittance that has improved such existing disadvantages. Still another object of the present invention is to provide a liquid crystal display device to which a stable high quality of display is given by using the film having a high transmittance or the polarizing plate.
Other and further objects, features, and advantages of the invention will appear more fully from the following description, taken in connection with the accompanying drawings.